ATP-binding cassette transporter G1 (ABCG1 or ABC8), the human homolog of the Drosophila white gene, has been reported to regulate macrophage cholesterol and phospholipid transport in vitro. However, to date the in vivo physiological function of ABCG1 has not been investigated. To elucidate the potential role of ABCG1 in lipoprotein metabolism in vivo, we generated recombinant adenovirus expressing human ABCG1 (rABCG1-AdV) and studied the effects of adenovirus-mediated ABCG1 gene transfer on the plasma lipid profile and HDL metabolism. We injected 5x108 pfu of rAdV-ABCG1 (n=7) and control Luciferase-rAdV (n=9) in C57BL mice. Baseline lipid levels in rABCG1-AdV injected mice were similar to rLucif-AdV control mice: TC=88+/-4 mg/dL, TG=63+/-8 mg/dL, PL=151+/-5 mg/dL, CE=77+/-4 mg/dL, and HDL-C=70+/-5 mg/dL. Day 4 after rAdV infusion changes in the baseline lipid profile were: TC (decreased by 12%; NS), CE (decreased by 27%; p<0.04), and HDL-C (decreased by 20%; p<0.05) in mice injected with rABCG1-AdV. The plasma CE/TC ratio and HDL-C/TC ratio were also decreased by -18% (p<0.02) and -43% (p<0.0001), respectively. The percent change in baseline TC and CE correlated in a dose-dependent manner with titer of injected rABCG1-AdV. FPLC analyses and lipid staining of native agarose gel on day 4 after virus injection showed a significant reduction in the HDL-C in mice expressing ABCG1 with no change in HDL size or electrophoretic mobility. Immunoblot analysis revealed decreased plasma apoA-I and apoA-II in rABCG1-AdV treated mice. Initial kinetic analyses using [3H]-CE HDL and [125I]-apoA-I HDL demonstrated that the plasma decay of HDL-CE and apoA-I-HDL in rABCG1-AdV injected mice was enhanced compared to controls. Hepatic and renal expression of SR-B1 and cubilin, assessed by immunoblotting was not changed following infusion of rABCG1-AdV. In summary: Adenovirus-mediated expression of human ABCG1 in mice alters the plasma lipid profile leading to decreased plasma HDL-C, CE and CE/TC ratio providing for the first time, evidence supporting an important role of ABCG1 in lipoprotein metabolism in vivo.